Strictly speaking you are right, my logic was flawed (hidden assumption). But let's stick with the orignal issue here, which is whether the test is predictive.

Agreed - this is why I asked whether there is any proof of its alleged predictive power.

Without this, I don't think it's reasonable to assume that it is in fact predictive.

Yes, but the point I'm trying to make is that the claim that any test has zero predicitive power is actually pretty bold.

For example, the simple test of whether a user clicks a certain link or not already has predicitive power (companies are using this, fruitfully). So a more sophisticated test like MBTI certainly has some predictive power.

This is a completely bogus argument. Phrenology[1] on its face sounds pretty sophisticated, but it still has zero predictive power.

[1] https://en.wikipedia.org/wiki/Phrenology

Read this: http://www.medicaldaily.com/how-birth-month-influences-perso...

Unless it is demonstrated to have some predictive power, it isn't certain at all.

Additionally, the added (relative) complexity doesn't imply anything about its qualities.